1. Field of the Invention
The present invention relates to a coating apparatus for a traveling web, and more particularly to a coating apparatus which applies coating liquids to the traveling web such as polymer film, paper support, metal strip, etc.
2. Description of the Related Art
A roll coater, an extrusion coater, a slide bead coater, a gravure coater, a bar coater, etc. are known as a coater which coats a traveling web with a coating solution. These coaters are selected according to the coating solution and the product.
The Japanese Patent Application Laid-open No. 63-69573 discloses a coater in which two or more coating heads are arranged in series in the longitudinal direction of a traveling web, and the coating heads are used alternately. The U.S. Pat. No. 3,899,112 discloses a coater, which uses coating heads selectively on a web path composed of rollers.
However, in the case of the above-mentioned conventional coater, it is difficult to apply many types of the coating solution under a variety of conditions by one coater.
For example, the roll coater and the bar coater are suitable for applying the web with a thin layer; but when the web is already coated with something, a problem tends to occur that the coated layer is damaged.
In the case of the extrusion coater, the coated layer is hardly damaged. However, some coating solution causes a problem in that the web cannot be coated evenly or cannot be applied with a thin layer.
Furthermore, in a coater with only one coating head, there exists disadvantage that plenty of time is required before starting to coat new solution which differs from previous coating solution, because it is necessary to clean the coating head and to prepare the new coating solution.
Therefore, in order to eliminate the above-mentioned disadvantages, two coating heads 1 and 2 are provided on the traveling path of the web 3 as shown in FIG. 13. For example, in the case when the coating head 2 is expected to be used by the method of the coating head 1, a web 3 is cut between a pass roller 4 and a pass roller 5, and the leading end of the web 3 is conveyed by being supported on a backup roller 7 via a pass roller 6, so that the coating head 2 can coat the web as shown in FIG. 14 (the Japanese Patent Application Laid-open No. 63-69573). However, this coater has a disadvantage in that it requires a lot of time for preparation because the web 3 should be cut every time the coating head is replaced, and the traveling path of the web 3 needs to be changed.
Moreover, the coating head may be provided in such a manner as to be installed and removed freely, and the coating head is selectively replaced according to the condition. However, the replacement of the coating head requires a lot of time, and it is difficult to install the coating head accurately.